FBX import overwrite changed textures

I have a weird problem on Unity 3.5 regarding a prefab issue: textures are overwrite by original stored in fbx every time.

I imported an fbx from 3ds max with embedded media textures.
I changed the textures substituting some of them with new one I created in GIMP and imported separately.

Then I created a prefab and moved all into it. Exported all in a unity package to be used in another project.


When I use the prefab in another project (importing the package) ALL is perfect INITIALLY… but as soon as I touch something Unity decides to reimport the original fbx and ASSIGN the old textures to the materials. And all the prefab customised textures just disappear !!

I cannot understand what is happening because Unity decides for me without explaining what is doing.
Overwrite of texture to include a logo is a very NORMAL behaviour… it worked in 3.4 and is working in the same project. Why not in all cases. What is different. Who is the author of a so bizar behaviour ?



I hope I found a reasonable solution.
If, in the prefax, I manually assign the textures to the materials then unity remembers and during reimport (any) of the fbx my assignments are kept.